JP7420001B2 - Method for producing metal cadmium - Google Patents

Description

The present invention relates to a method for producing metal cadmium.

Zinc oxide ore obtained by separating and recovering impurities from crude zinc oxide and the like is widely used as a raw material for zinc ingots in zinc smelters. This crude zinc oxide can be obtained, for example, from steel dust generated from steelmaking furnaces such as blast furnaces and electric furnaces in the steel industry through reduction roasting treatment. Reuse as a resource is desirable.

On the other hand, such crude zinc oxide derived from steel dust contains a high proportion of halogen components such as chlorine and fluorine, and impurities such as cadmium, in addition to its main component, zinc oxide. Among these impurities, cadmium in particular is a toxic metal, so cadmium is generally separated and recovered in zinc oxide manufacturing plants.
When separating and recovering cadmium, a wet process is generally employed, for example, in which metal cadmium is obtained by subjecting steel dust to acid and performing zinc cementation on the leachate from which cadmium is leached. However, the metal cadmium obtained through such wet processing often contains impurities such as zinc, lead, copper, and manganese that are undesirable as electronic materials. For this reason, metal cadmium has been subjected to dry treatment after wet treatment to remove these impurities, but dry treatment is undesirable from the viewpoint of environmental considerations and rationalization of energy use, and wet treatment A new processing method to obtain high-purity metal cadmium is being explored.

For example, the treatment method disclosed in Patent Document 1 involves electrolytically winning cadmium hydroxide obtained by neutralizing an aqueous solution containing cadmium and copper with an alkali, adding an alkali to remove copper after acid leaching. This is a processing method for obtaining metallic cadmium.
However, the copper grade of copper, which is an impurity in the obtained metallic cadmium, is 1.2 mass% or 2.4 mass%, and highly pure metallic cadmium with reduced impurities has not been obtained.

Japanese Patent Application Publication No. 2012-77374

The present invention was made in view of the above circumstances, and it is possible to extract Cd>95mass%, Mn, Pb, The present invention provides a manufacturing method for obtaining highly pure metallic cadmium in which the grades of Cu, Ni, and Tl are each ≦0.02 mass% and Zn≦1 mass%.

In a first aspect of the present invention, an alkali is added to a raw material solution containing cadmium, and the cadmium contained in the raw material solution forms cadmium hydroxide to become a cadmium precipitate containing the cadmium hydroxide. After adjusting the pH of the raw material solution within a range to form a neutralized slurry containing the cadmium precipitate, the neutralized slurry is subjected to solid-liquid separation treatment to obtain the cadmium precipitate containing the cadmium hydroxide. a neutralization step, and adding an acid to the cadmium precipitate to adjust the pH to a range where cadmium in the cadmium precipitate is leached to form a cadmium-containing leaching slurry; A leaching step in which the slurry is subjected to solid-liquid separation treatment to obtain a leachate containing cadmium; and a leaching step in which zinc powder is added to the leachate to precipitate lead and copper as precipitates of metallic lead and copper; After forming the cementation slurry, a partial cementation step in which the cementation slurry is subjected to solid-liquid separation treatment to obtain an electrolytic starting solution in which copper and lead are reduced in the solid matter including the precipitate and the liquid phase; The cathode and anode are immersed in an electrolytic tank filled with electrolytic starting solution, and while cadmium is deposited on the cathode to become metal cadmium, the amount of zinc deposited is 1 mass% or less, and the amount of nickel and thallium deposited is 0.02 mass%. This method of producing metal cadmium is characterized by comprising an electrowinning step of obtaining the metal cadmium by adjusting the current density and the cadmium concentration of the electrolytic solution at the end of electrolysis within a range suppressed below.

A second aspect of the present invention is that the leaching step in the first aspect adds an acid to the cadmium precipitate and adjusts the pH to a range where cadmium in the cadmium precipitate is leached out. After forming a leaching slurry containing cadmium, an oxidizing agent is added to the cadmium-containing leaching slurry, and the redox potential is adjusted to a range in which manganese oxide is formed. This is a method for producing metal cadmium, characterized in that it is a step of subjecting a slurry to solid-liquid separation treatment to obtain a leachate containing cadmium with reduced manganese.

A third invention of the present invention is a method for producing metal cadmium, characterized in that the redox potential in the second invention is adjusted to a range of 1000 mV or more (vs. Ag/AgCl).

A fourth invention of the present invention is characterized in that the amount of zinc powder added in the first to third inventions is adjusted to a range of 0.2 g/L or more and 5 g/L or less. This is the manufacturing method.

A fifth invention of the present invention is that the current density in the first to fourth inventions is adjusted to a range of 50 A/m ² or more and 2000 A/m ² or less, and the cadmium concentration of the electrolyte at the end of the electrolysis is This is a method for producing metal cadmium, characterized in that the content is adjusted to a range of 1.0 g/L or more and 3.0 g/L or less.

In a sixth aspect of the present invention, the current density in the first to fourth aspects is adjusted to a range of 50 A/m ² or more and 150 A/m ² or less, and the cadmium concentration of the electrolyte at the end of the electrolysis is 1. This is a method for producing metal cadmium, characterized in that the content is adjusted to a range of .0 g/L or more and 3.0 g/L or less.

A seventh invention of the present invention is that the neutralization step in the first to sixth inventions is comprised of a first pH adjustment step and a second pH adjustment step, and the first pH adjustment step and the second This method of producing metal cadmium is characterized in that the pH adjustment steps are performed in the following order.

An eighth invention of the present invention is that the raw material solution containing cadmium in the first to seventh inventions has a cadmium concentration of 0.05 g/L or more, a zinc concentration of 5 g/L or less, and a copper concentration of 0. Cadmium metal characterized by having a lead concentration of 1 g/L or less, a manganese concentration of 1 g/L or less, a nickel concentration of 0.005 g/L or less, and a thallium concentration of 0.05 g/L or less. This is a manufacturing method.

According to the method for producing metallic cadmium of the present invention, it is possible to obtain highly pure metallic cadmium with Cd > 95 mass%, Mn, Pb, Cu, Ni, and Tl grades of ≦0.02 mass% and Zn≦1 mass%, respectively. , its industrial value is extremely large.

It is a manufacturing process diagram of metal cadmium to which the present invention is applied.

The method for producing cadmium metal of the present invention is a method for producing cadmium metal in which highly pure cadmium metal is obtained using a raw material solution containing cadmium as a starting material.
As shown in Figure 1, the method consists of four steps: neutralization step, leaching step, partial cementation step, and electrowinning step. It is possible to produce high-purity metal cadmium which contains manganese, lead, copper, nickel, and thallium in a grade of 0.02 mass% or less, and has a zinc grade of 1 mass% or less.
Each process will be explained below.

<Neutralization process>
In the neutralization step, an alkali is added to a raw material solution containing cadmium, and the raw material is added to a range where cadmium contained in the raw material solution forms cadmium hydroxide and becomes a cadmium precipitate containing the cadmium hydroxide. After adjusting the pH of the solution to form a neutralized slurry containing the cadmium precipitate, the neutralized slurry is subjected to solid-liquid separation treatment to obtain the cadmium precipitate containing the cadmium hydroxide.

Here, the raw material solution desirably has a cadmium concentration of 0.05 g/L or more, a zinc concentration of 5 g/L or less, a copper concentration of 0.1 g/L or less, a lead concentration of 1 g/L or less, The raw material solution has a composition in which the manganese concentration is 1 g/L or less, the nickel concentration is 0.005 g/L or less, and the thallium concentration is 0.05 g/L or less. A raw material solution that satisfies this composition range can effectively carry out subsequent steps, and has the same composition range as the previous raw material solution except that it contains a higher manganese concentration of 10 g/L or less. It is possible to effectively produce metal cadmium even from a raw material solution exhibiting the following by using the second embodiment described below.

Now, when carrying out this neutralization step, the adjustment range is not particularly limited as long as the pH is adjusted to a range in which cadmium forms cadmium hydroxide and becomes a precipitate. For example, the pH may be adjusted to a range of 8.5 or higher. Thereby, it is possible to efficiently precipitate cadmium hydroxide. As the pH adjuster used for pH adjustment, any industrially usable alkali can be used. For example, in addition to calcium hydroxide, sodium hydroxide, magnesium hydroxide, potassium hydroxide, etc. may be used.

Note that, in order to effectively increase the concentration of cadmium contained in the cadmium precipitate, this neutralization step may be performed separately in the order of a first pH adjustment step and a second pH adjustment step.

(First pH adjustment step)
In the first pH adjustment step, a pH adjuster is added to the raw material solution containing cadmium, and the pH of the raw material solution is adjusted to a range where zinc and lead form hydroxide and become a precipitate. A first neutralized slurry consisting of a precipitate of zinc and lead hydroxide and a filtrate is formed, and this first neutralized slurry is separated into solid and liquid to remove the precipitate of zinc and lead hydroxide from the system. This is a step to obtain a filtrate containing cadmium.

In this case, the adjustment range is not particularly limited as long as the pH is adjusted to a range in which the zinc and lead form hydroxides and become precipitates. For example, the pH may be adjusted to a range of 7.0 or more and 9.0 or less. Thereby, it is possible to preferentially precipitate and separate zinc and lead.

(Second pH adjustment step)
In the second pH adjustment step, a pH adjuster is further added to the filtrate obtained in the first pH adjustment step of the previous step, and the cadmium contained in the filtrate forms cadmium hydroxide to form the cadmium water. By adjusting the pH of the filtrate to a range that results in cadmium precipitates containing oxides, a second neutralized slurry in which the cadmium hydroxide is distributed in the solid phase is formed, and this second neutralized slurry is solidified. This is a step of liquid separation to obtain a cadmium precipitate containing the cadmium hydroxide.

In this case, the pH is adjusted to be higher than the pH of the filtrate adjusted in the first pH adjustment step.
In this adjustment, the adjustment range is not particularly limited as long as the pH is adjusted to a range in which cadmium contained in the filtrate forms cadmium hydroxide. For example, the pH may be adjusted to a range of 8.5 or higher. Thereby, it is possible to perform precipitation separation effectively. Moreover, by further adjusting the pH to a range of 11.0 or less in the above, even if the filtrate contains thallium, it is possible to effectively distribute thallium into the liquid.

<Leaching process>
In the leaching step, acid is added to an aqueous solution or slurry prepared by adding water to the cadmium precipitate containing cadmium hydroxide obtained in the previous neutralization step to preferentially leach cadmium. , other components other than cadmium are impurities and are distributed into the solid form of hydroxide and sulfate, which is solid-liquid separated to form a leaching slurry in which cadmium is leached, and this leaching slurry is subjected to solid-liquid separation. This is the process of obtaining a leachate from which cadmium has been leached.

In this case, the acid used is not particularly limited, and for example, sulfuric acid can be used. Moreover, the adjustment range of the pH of the leachate is not particularly limited as long as it is a pH at which cadmium is preferentially leached out. For example, the pH may be adjusted to a range of 2.0 or more and pH 5.0 or less. This allows cadmium to be effectively leached out.

The leachate thus obtained has, for example, a cadmium concentration of 20 g/L or more, a zinc concentration of 50 g/L or less, a manganese concentration of 2 g/L or less, a lead concentration of 0.5 g/L or less, and a copper concentration of 0. The leachate has a composition of 1 g/L or less, a nickel concentration of less than 0.2 g/L, and a thallium concentration of less than 0.1 g/L. If the pH is adjusted to a range exceeding 5.0, cadmium will not be sufficiently leached, and if the pH is adjusted to a range below 2.0, a large amount of acid will be consumed, but the leaching rate of cadmium will hardly improve, which is inefficient. .

Furthermore, when using a raw material solution that has the same composition range as the previous raw material solution, except that the raw material solution has a manganese concentration of 10 g/L or less and contains more manganese, A leachate may be obtained by further performing an oxidation treatment. (An embodiment in which the leaching slurry is further subjected to oxidation treatment is referred to as a second embodiment.)
Now, in this second embodiment, an oxidizing agent is added to the leaching slurry, the redox potential is adjusted to a range in which the manganese contained in the leaching slurry becomes manganese oxide, and the manganese oxide is converted into a precipitate. After forming an oxidized slurry containing the oxidized slurry, a leachate is obtained by subjecting the oxidized slurry to solid-liquid separation. The leachate obtained in this manner is a leachate in which cadmium has been leached out and manganese contained as manganese oxide has been removed, so that the amount of manganese is reduced.

Since most of the manganese is removed through the leaching step or the leaching step including oxidation treatment, it is possible to effectively suppress the precipitation of manganese on the anode in the electrowinning step described below. This prevents the contamination of manganese into metal cadmium by cleaning the anode surface every time electrowinning is performed, and by installing a tray in the electrolytic cell to catch the manganese oxide that falls off the anode during electrowinning. No measures are required to prevent this, and efficient electrowinning becomes possible.

Note that when adding the oxidizing agent in the second embodiment, the oxidizing agent used is not particularly limited, and for example, sodium hypochlorite can be used. Further, the adjustment range of the amount of the oxidizing agent added is not particularly limited as long as it is within a range where the redox potential is such that manganese precipitates as manganese oxide. For example, the redox potential may be adjusted to a range of 1000 mV or more (vs. Ag/AgCl). This allows manganese to be effectively precipitated as an oxide.

In this way, the leachate obtained through the leaching process including oxidation treatment is a leachate from which manganese has been highly removed. A leachate having a composition of .005 g/L or less, a lead concentration of 0.5 g/L or less, a copper concentration of 0.1 g/L or less, a nickel concentration of less than 0.2 g/L, and a thallium concentration of less than 0.1 g/L. It is.

<Partial cementation process>
In the partial cementation process, zinc powder is added to the cadmium-leached leachate obtained in the previous leaching process to precipitate lead and copper as metals, creating a cementation slurry containing lead and copper as precipitates. After forming, this cementation slurry is separated into solid and liquid to obtain an electrolytic starting solution from which lead and copper have been removed.
In this case, the amount of zinc powder added is not particularly limited; You can adjust it to the following range.

As a result, the lead and copper contained in the leachate obtained in the partial cementation process are effectively precipitated as metallic lead and metallic copper, respectively, and the lead and copper contained in the leachate are reduced to less than 0.005 g/L. However, it is possible to allow 50% or more of the cadmium contained in the leachate to remain. The solution obtained in this way has, for example, a cadmium concentration of 10 g/L or more, a zinc concentration of 55 g/L or less, and a manganese concentration of less than 2 g/L (in the above leaching step, manganese is removed by adding an oxidizing agent). The solution has a composition of less than 0.005 g/L), a lead concentration of less than 0.005 g/L, and a copper concentration of less than 0.005 g/L, and is preferable as an electrolysis starting solution in the electrowinning process described below. can be used.
Note that when adding zinc powder, it is preferable to keep the amount of zinc powder added as low as possible to remove lead and copper, and then apply the electrowinning step described below. This makes it possible to suppress the amount of zinc used in the precipitation of metal cadmium, making it possible to efficiently collect metal cadmium.

<Electrowinning process>
In the electrowinning process, the anode and cathode are immersed in an electrolytic tank filled with the electrolytic starting solution obtained in the partial cementation process in the previous process, and cadmium is deposited on the cathode to become metallic cadmium, while zinc is deposited. In this process, metal cadmium is electrolytically extracted by adjusting the current density and the cadmium concentration of the electrolytic solution at the end of electrolysis to a range where the electrolysis is suppressed. The obtained metal cadmium is recovered by, for example, vibrating the cathode on which metal cadmium has been deposited to cause the metal cadmium to fall off the cathode, and extracting it from the bottom of the electrolytic cell.

Here, as the cathode, for example, a SUS plate or an Al plate which is excellent in electrical conductivity and cost can be used. Further, as the anode, for example, an electrode for oxygen generation can be used. By using the oxygen generating electrode, it is possible to effectively suppress the generation of chlorine at the anode. If chlorine is generated at the anode, the metal cadmium deposited at the cathode will be reoxidized, that is, redissolved, which is inefficient.

Further, as the oxygen generating electrode, for example, a DSE oxygen generating electrode manufactured by De Nora Permelec Co., Ltd. can be employed. Further, by covering the anode with a filter cloth or the like to block generated chlorine from the cathode, it is possible to effectively suppress the diffusion of chlorine generated at the anode to the vicinity of the cathode.

Now, when adjusting the current density of this electrowinning and the cadmium concentration of the electrolyte at the end of electrolysis, the adjustment range is as long as the amount of zinc precipitation is 1 mass% or less, and the amount of nickel and thallium precipitation is 0.02 mass% or less. is not particularly limited. For example, the current density may be adjusted to a range of 50 A/m ² or more and 2000 A/m ² or less. In addition, in the above current density range, by adjusting the cadmium concentration of the electrolyte at the end of electrolysis to a range of 1.0 g/L or more and 3.0 g/L or less, the precipitation of zinc, nickel, and thallium can be effectively suppressed. It is possible to suppress the

The metal cadmium obtained in this way has, for example, a purity of more than 95 mass%, a composition in which manganese, lead, copper, nickel, and thallium are each 0.02 mass% or less, and zinc is 1 mass% or less. It is a metal cadmium. If it exceeds 2000 A/m ² , there is a risk that zinc will be deposited together with cadmium, and if it is less than 50 A/m ² , the amount of electrodeposition will be insufficient, resulting in inefficiency.

When adjusting the current density, the precipitation of zinc, nickel, and thallium can be further suppressed by adjusting the current density to a range of 50 A/m ² or more and 150 A/m ² or less. In this case, the precipitation of zinc, nickel, and thallium can be more effectively suppressed by adjusting the cadmium concentration of the electrolyte at the end of electrolysis to a range of 1.0 g/L or more and 3.0 g/L or less. It is possible to do so.
The metal cadmium obtained in this way is a higher purity metal cadmium, for example, has a purity of 99.9 mass% or more, and has manganese, lead, copper, nickel, and thallium grades of 0.01 mass% or less each, and zinc. It is extremely pure metal cadmium with a composition of 0.05 mass% or less.

By the way, when the manganese concentration in the electrolytic starting solution is 0.1 g/L or more, manganese oxide is precipitated at the anode, which acts as a catalyst for oxygen generation and may suppress the generation of chlorine. Manganese oxides may fall to the bottom of the electrolyzer and mix with the metal cadmium. For this reason, during electrowinning, for example, it is necessary to clean the anode surface each time to remove manganese oxide on the anode surface, or to remove the manganese oxide that falls off from the anode during electrowinning in the electrolytic cell. It is preferable to take measures such as installing the

On the other hand, in the case of the second embodiment in which manganese is removed by adding an oxidizing agent in the leaching process, the manganese concentration in the electrolytic starting solution is extremely low, so that the manganese oxide in the anode is Precipitation is effectively suppressed. This is done by cleaning the anode surface every time electrowinning is performed, and by installing a tray in the electrolytic cell to catch the manganese oxide that falls off from the anode during electrowinning, to prevent manganese from getting mixed into the metal cadmium. This means that no preventive measures are required. This makes it possible to efficiently obtain highly pure metal cadmium without interrupting work.

The details will be explained below using examples.

A raw material solution having the composition shown in Table 1 was prepared.

Next, calcium hydroxide powder was added to the fractionated raw material solution while stirring at room temperature of 25°C, the pH was adjusted to 8.0, and the mixture was kept stirring for 60 minutes to generate a precipitate. A first neutralized slurry containing a precipitate was obtained. This first neutralized slurry was filtered through membrane filter paper to separate it into a precipitate and a filtrate.
Subsequently, the above filtrate was collected, and while stirring at room temperature of 25°C, the pH was adjusted to 11.0 by adding calcium hydroxide powder, and the pH was adjusted to 11.0 by stirring for 60 minutes to remove cadmium hydroxide. A second neutralized slurry containing the precipitate was obtained. This second neutralized slurry was filtered and collected using membrane filter paper to obtain a precipitate containing cadmium hydroxide.

Next, 40 g of the precipitate containing cadmium hydroxide was taken into a 200 ml beaker, and 65 ml of pure water was added to the cadmium hydroxide, and while stirring at room temperature of 25°C, the pH was adjusted to 4.0. 64% by mass of sulfuric acid was added thereto, and after the pH was stabilized, the mixture was stirred for 60 minutes to obtain a leaching slurry.
To this leaching slurry, sodium hypochlorite was further added until the redox potential became 1100 mV (vs. Ag/AgCl) to obtain an oxidized slurry.
This oxidized slurry was filtered through membrane filter paper, and the composition of the filtrate (leachate) was analyzed. The analysis results are shown in Table 2.

It was confirmed that cadmium was highly concentrated. It was also confirmed that while manganese was removed, other impurities remained.
Next, zinc powder was added in an amount of 1.0 g/L while stirring the leachate to generate a precipitate containing lead and copper as metal bodies, and a cementation slurry containing this precipitate was obtained. . This cementation slurry was filtered through membrane filter paper, and the composition of the filtrate (electrolytic starting solution) was analyzed. The analysis results are shown in Table 3.

It was confirmed that the cadmium concentration was maintained at a high concentration even after the addition of zinc powder, and the concentrations of lead and copper were both reduced to less than 0.005 g/L.
Next, a SUS plate made of SUS304 with an opening of 5 cm square was added as a cathode to the electrolytic starting solution, and an oxygen generation electrode (DSE oxygen generation electrode manufactured by De Nora Permelec Co., Ltd.) with an opening of 5 cm square was added as an anode. The sample was immersed, and electrowinning was carried out at a current density of 150 A/m ² (0.375 A). When the cadmium concentration in the electrolytic solution reached 1.0 g/L, electrowinning was completed, the cathode was taken out from the electrolytic cell, the electrodeposited metal cadmium was stripped off, and the impurity quality of the obtained metal cadmium was analyzed. .
The analysis results are shown in Table 4. In addition, the cadmium quality was determined from this analysis result. The results are shown in Table 5.

The obtained metal cadmium has a purity of more than 95 mass%, and satisfies the quality level of manganese, lead, copper, nickel, and thallium of 0.02 mass% or less, and zinc content of 1 mass% or less, and further is an extremely high-purity metal cadmium with a purity of 99.9 mass% or more, a manganese, lead, copper, nickel, and thallium grade of 0.01 mass% or less, and a zinc grade of 0.05 mass% or less. Ta.

Next, the anode was taken out from the electrolytic bath and the surface condition of the anode was checked.
No manganese oxide was deposited on the surface of the anode. This means that there is no need to take measures to prevent manganese from being mixed into cadmium metal, and electrolytic winning can be carried out efficiently without interrupting work.

The same procedure as in Example 1 was conducted except that the current density during electrowinning was adjusted to 600 A/m ² (1.5 A). Table 6 shows the analysis results of the impurity level of the obtained metal cadmium. In addition, the cadmium quality was determined from this analysis result. The results are shown in Table 7.

The obtained metallic cadmium is highly pure metallic cadmium with a purity of more than 95 mass%, a grade of manganese, lead, copper, nickel, and thallium of 0.02 mass% or less, and a zinc grade of 1 mass% or less. was.
Next, the anode was taken out from the electrolytic bath and the surface condition of the anode was checked. As in Example 1, no manganese oxide was deposited on the surface of the anode.

The same conditions as in Example 1 were conducted except that sodium hypochlorite was not added to the leaching slurry to form an oxidized slurry.
As a result, as in Example 1, the purity was 99.9 mass% or more, the grades of manganese, lead, copper, nickel, and thallium were each 0.01 mass% or less, and the zinc content was 0.05 mass% or less. Highly pure metallic cadmium was obtained.

Furthermore, when we took the anode out of the electrolytic bath and checked the surface condition of the anode, we found that manganese oxide had been deposited on the surface of the anode. It can also be applied in actual operations by taking measures to prevent manganese from being mixed into metal cadmium, such as installing a tray in the electrolytic cell for manganese oxide that falls off from the anode. be.

(Comparative example 1)
The process was carried out under the same conditions as in Example 1, except that the partial cementation step was not carried out.
Table 8 shows the analysis results of the impurity level of the obtained metal cadmium. In addition, the cadmium quality was determined from this analysis result.
The results are shown in Table 9.

The obtained metal cadmium had a purity of over 95 mass%, and the grades of manganese, copper, nickel, and thallium were each 0.02 mass% or less, and the zinc content was 1 mass% or less, but the lead content was 0.02 mass% or less. It has exceeded 0.02 mass%.

(Comparative example 2)
The same procedure as in Example 1 was conducted except that the current density during electrowinning was adjusted to 3000 A/m ² (7.5 A). Table 10 shows the analysis results of the impurity level of the obtained metal cadmium. In addition, the cadmium quality was determined from this analysis result. The results are shown in Table 11.

The obtained metal cadmium had a purity of over 95 mass%, and the manganese, lead, copper, and thallium grades were each 0.02 mass% or less, but the nickel content exceeded 0.02 mass%, and the zinc It has also exceeded 1 mass%.

By going through each process of the present invention, the composition has a purity of over 95 mass%, a grade of manganese, lead, copper, nickel, and thallium of 0.02 mass% or less, and a zinc grade of 1 mass% or less. It was confirmed that metallic cadmium was obtained.

Claims (8)

An alkali is added to the raw material solution containing cadmium, and the pH of the raw material solution is adjusted to a range in which cadmium contained in the raw material solution forms cadmium hydroxide and becomes a cadmium precipitate containing the cadmium hydroxide. to form a neutralized slurry containing the cadmium precipitate, and then subjecting the neutralized slurry to a solid-liquid separation treatment to obtain a cadmium precipitate containing the cadmium hydroxide;
An acid is added to the cadmium precipitate to adjust the pH to a range where cadmium in the cadmium precipitate is leached out to form a leaching slurry containing cadmium, and then solid-liquid separation is performed to form the cadmium-containing leaching slurry. a leaching process to obtain a cadmium-containing leachate;
Adding zinc powder to the leachate to precipitate lead and copper as a precipitate of metallic lead and metallic copper to form a cementation slurry containing the precipitate, and then subjecting the cementation slurry to a solid-liquid separation treatment, a partial cementation step for obtaining an electrolytic starting solution in which the solid material including the precipitate and the liquid phase are reduced in copper and lead;
A cathode and an anode are immersed in an electrolytic tank filled with the electrolytic starting solution, and cadmium is deposited on the cathode to become metal cadmium, while the amount of zinc deposited is 1 mass% or less, and the amount of nickel and thallium deposited is 0.02 mass%. % or less, an electrowinning step of obtaining the metal cadmium by adjusting the current density and the cadmium concentration of the electrolytic solution at the end of the electrolysis;
A method for producing cadmium metal, comprising: After the leaching step adds an acid to the cadmium precipitate and adjusts the pH to a range where cadmium in the cadmium precipitate is leached to form a cadmium-containing leaching slurry,
An oxidizing agent is added to the cadmium-containing leaching slurry, and the redox potential is adjusted to a range in which manganese oxide is formed, and the oxidized slurry containing the manganese oxide precipitate is subjected to a solid-liquid separation treatment. , the step is to obtain a leachate containing cadmium with reduced manganese;
The method for producing metal cadmium according to claim 1, characterized by: The redox potential is adjusted to a range of 1000 mV or more (vs. Ag/AgCl);
The method for producing metal cadmium according to claim 2, characterized by: The amount of the zinc powder added is adjusted to a range of 0.2 g/L or more and 5 g/L or less;
The method for producing metal cadmium according to any one of claims 1 to 3, characterized by: The current density is adjusted to a range of 50 A/m ² or more and 2000 A/m ² or less,
The cadmium concentration of the electrolyte at the end of the electrolysis is adjusted to a range of 1.0 g/L or more and 3.0 g/L or less;
The method for producing metal cadmium according to any one of claims 1 to 4, characterized by: The current density is adjusted to a range of 50 A/m ² or more and 150 A/m ² or less,
The cadmium concentration of the electrolyte at the end of the electrolysis is adjusted to a range of 1.0 g/L or more and 3.0 g/L or less;
The method for producing metal cadmium according to any one of claims 1 to 4, characterized by: The neutralization step is composed of a first pH adjustment step and a second pH adjustment step, and the first pH adjustment step and the second pH adjustment step are performed in this order;
The method for producing metal cadmium according to any one of claims 1 to 6, characterized by: The raw material solution containing cadmium has a cadmium concentration of 0.05 g/L or more, a zinc concentration of 5 g/L or less, a copper concentration of 0.1 g/L or less, a lead concentration of 1 g/L or less, and a manganese concentration. is 1 g/L or less, the nickel concentration is 0.005 g/L or less, and the thallium concentration is 0.05 g/L or less,
The method for producing metal cadmium according to any one of claims 1 to 7, characterized by:

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